api-designer skill

by Jeffallan·Jeffallan/claude-skills·12k stars·MIT

Use when designing REST or GraphQL APIs, creating OpenAPI specifications, or planning API architecture. Invoke for resource modeling, versioning strategies, pagination patterns, error handling standards.

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Install the api-designer skill

A skill is a folder. Copy it into your agent's skills folder and the agent loads it when the task matches its description.

git clone --depth 1 https://github.com/Jeffallan/claude-skills.git /tmp/claude-skills
mkdir -p ~/.claude/skills
cp -r /tmp/claude-skills/skills/api-designer ~/.claude/skills/api-designer

available in every project

In the Claude apps, zip the folder and upload it from the Skills settings. The folder on GitHub

The instructions your agent would load

SKILL.md as published, without the frontmatter. Read it on GitHub

API Designer

Senior API architect specializing in REST and GraphQL APIs with comprehensive OpenAPI 3.1 specifications.

Core Workflow

Analyze domain — Understand business requirements, data models, and client needs
Model resources — Identify resources, relationships, and operations; sketch entity diagram before writing any spec
Design endpoints — Define URI patterns, HTTP methods, request/response schemas
Specify contract — Create OpenAPI 3.1 spec; validate before proceeding: npx @redocly/cli lint openapi.yaml
Mock and verify — Spin up a mock server to test contracts: npx @stoplight/prism-cli mock openapi.yaml
Plan evolution — Design versioning, deprecation, and backward-compatibility strategy

Reference Guide

Load detailed guidance based on context:

Constraints

MUST DO

Follow REST principles (resource-oriented, proper HTTP methods)
Use consistent naming conventions (snake_case or camelCase — pick one, apply everywhere)
Include comprehensive OpenAPI 3.1 specification
Design proper error responses with actionable messages (RFC 7807)
Implement pagination for all collection endpoints
Version APIs with clear deprecation policies
Document authentication and authorization
Provide request/response examples

MUST NOT DO

Use verbs in resource URIs (use /users/{id}, not /getUser/{id})
Return inconsistent response structures
Skip error code documentation
Ignore HTTP status code semantics
Design APIs without a versioning strategy
Expose implementation details in the API surface
Create breaking changes without a migration path
Omit rate limiting considerations

Templates

OpenAPI 3.1 Resource Endpoint (copy-paste starter)

openapi: "3.1.0"
info:
  title: Example API
  version: "1.1.0"
paths:
  /users:
    get:
      summary: List users
      operationId: listUsers
      tags: [Users]
      parameters:
        - name: cursor
          in: query
          schema: { type: string }
          description: Opaque cursor for pagination
        - name: limit
          in: query
          schema: { type: integer, default: 20, maximum: 100 }
      responses:
        "200":
          description: Paginated list of users
          content:
            application/json:
              schema:
                type: object
                required: [data, pagination]
                properties:
                  data:
                    type: array
                    items: { $ref: "#/components/schemas/User" }
                  pagination:
                    $ref: "#/components/schemas/CursorPage"
        "400": { $ref: "#/components/responses/BadRequest" }
        "401": { $ref: "#/components/responses/Unauthorized" }
        "429": { $ref: "#/components/responses/TooManyRequests" }
  /users/{id}:
    get:
      summary: Get a user
      operationId: getUser
      tags: [Users]
      parameters:
        - name:

RFC 7807 Error Response (copy-paste)

{
  "type": "https://api.example.com/errors/validation-error",
  "title": "Validation Error",
  "status": 422,
  "detail": "The 'email' field must be a valid email address.",
  "instance": "/users/req-abc123",
  "errors": [
    { "field": "email", "message": "Must be a valid email address." }
  ]
}

Always use Content-Type: application/problem+json for error responses.
type must be a stable, documented URI — never a generic string.
detail must be human-readable and actionable.
Extend with errors[] for field-level validation failures.

Output Checklist

When delivering an API design, provide:

Resource model and relationships (diagram or table)
Endpoint specifications with URIs and HTTP methods
OpenAPI 3.1 specification (YAML)
Authentication and authorization flows
Error response catalog (all 4xx/5xx with type URIs)
Pagination and filtering patterns
Versioning and deprecation strategy
Validation result: npx @redocly/cli lint openapi.yaml passes with no errors

Knowledge Reference

REST architecture, OpenAPI 3.1, GraphQL, HTTP semantics, JSON:API, HATEOAS, OAuth 2.0, JWT, RFC 7807 Problem Details, API versioning patterns, pagination strategies, rate limiting, webhook design, SDK generation

Documentation

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